1. Field of the Invention
The present invention relates to a method of searching for a motion vector, a method of generating a frame interpolation image by motion compensation using the motion vector, and a display system.
2. Description of the Related Art
Generally, there is two kinds of display units, one is an impulse type display unit that continues emitting light only by afterglow of a fluorescent substance after writing of an image, for example, CRT or field emission type display unit (FED), and the other is a hold type display unit that continues holding display of a previous frame till a new image is written, for example, Liquid Crystal Display (LCD) and Electro Luminescence Display (ELD).
A problem of the hold type display unit is a blur phenomenon occurring in a motion video display. The occurrence of the blur phenomenon appears a moving object over a plurality of frames. When the eyes of a viewer follow movement of the moving object, the images of a plurality of frames are overlapped and projected on the retina. The image of the same previous frame is continuously displayed while a display image is replaced from a previous frame to a next frame. In spite of this, the viewer predicts the image of the next frame, and observes the moving object while moving the eyes on the previous frame image in a moving direction of the moving object. In other words, since the following motion of the eyes has continuity and the eyes samples the image at a finer distance than the distance between frames, the viewer recognizes visually the image to interpolate adjacent frames. Therefore, the moving body is observed in blur.
Another problem of the hold type display unit is to occur unnatural movement when a motion video of few frames is displayed.
A display frame distance may be shorten to solve these problems. As a concrete technique it is considered to interpolate adjacent frames using a motion compensation used in MPEG (Motion Picture Experts Group phase 2) to form an interpolation image. In the motion compensation, a motion vector detected by block matching is used. However, since MPEG2 makes an image in units of a block, correlated blocks and uncorrelated blocks occur in the block. For this reason, a block distortion occurs due to uncorrelated blocks.
Japanese Patent Laid-Open No. 2000-224593 discloses an interframe interpolation method for solving this problem. According to this prior method, when the pixel value of an interpolation block in an interpolation frame is determined, the absolute difference value between two frames is compared with the threshold every corresponding pixel with respect to a to-be-decoded block. The blocks are classified into a first pixel region having an absolute difference value not more than the threshold and a second pixel region having an absolute difference value higher than threshold. In the first pixel region, an average of a pixel value of the first pixel region and a corresponding pixel value within a reference block designated by a motion vector between two frames is calculated to form an interpolation frame. In the second pixel region, a hidden surface relation in a to-be-decoded frame is determined, and a motion vector search direction between two frames is again set to detect a second motion vector. When a motion vector obtained by scaling the second motion vector designates a block, a pixel value in the search reference frame is copied to an interpolation frame.
It is an object of the present invention to provide a motion vector detection method suitable for creation of an interpolation image, a frame interpolation image making method using this method and a display system.